provided truly exceptional implementation support and research assistance. Financial support from the Overdeck Family Foundation and the Eli and Edythe Broad Foundation is gratefully acknowledged.

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provided excellent project management and research assistance. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research. NBER working papers are circulated for discussion and comment purposes. They have not been peer-reviewed or been subject to the review by the NBER Board of Directors that accompanies official NBER publications.